Abstract

The growth of $R_{1-x}$ $Pb_xMnO_3$ (R=La, Nd, [La,Nd]) single crystals by $PbO/PbF_2$ flux is described with optimized growth conditions. The structure of $Nd_{1-x}$ $Pb_xMnO_3$ changes from orthorhombic (x=0, Pnma) to tetragonal (x=0.25, P4/mmm) to cubic (x=0.38, Pm3¯m) as x increases. These changes are attributed to the progressive removal of inter-octahedral tilting and minimization of octahedral distortion leading to a higher symmetry as doping concentration increases. The $T_C$ of this system increases from 110 to 192 K for Pb concentration varying from x=0.15 to 0.42. The $T_{MI}$ also follows a similar trend. It is observed that $\langle r_A\rangle$ and $\sigma^2$ are the controlling parameters which influence the transport and magnetic properties of $La_{0.7-y}Nd_yPb_{0.3}MnO_3$. The presence of spin wave excitations are observed prominently in $La_{0.7}Pb_{0.3}MnO_3$ at low-temperature which is not so in case of Nd-based compounds. The total magnetic moments of all the Nd-based systems at low-temperature are influenced by Nd. The low-temperature specific heat data of $La_{0.7-y}Nd_yPb_{0.3}$ $MnO_3$ is analyzed and contributions of different mechanisms are discussed. It is noticed that the Schottky anomaly is present in specific heat at low-temperature only in Nd-based compounds.